Our best theory of nature has imaginary numbers at its heart. Making quantum physics more real conjures up a monstrous entity pulling the universe's strings
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IF YOU'VE ever tried counting yourself to sleep, it's unlikely you did it using the square roots of sheep. The square root of a sheep is not something that seems to make much sense. You could, in theory, perform all sorts of arithmetical operations with them: add them, subtract them, multiply them. But it is hard to see why you would want to.
All the odder, then, that this is exactly what physicists do to make sense of reality. Except not with sheep. Their basic numerical building block is a similarly nonsensical concept: the square root of minus 1.
This is not a "real" number you can count and measure stuff with. You can't work out whether it's divisible by 2, or less than 10. Yet it is there, everywhere, in the mathematics of our most successful – and supremely bamboozling – theory of the world: quantum theory.
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